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<center><h1>ThreeSum.java</h1></center><p><br>

Below is the syntax highlighted version of <a href = "ThreeSum.java">ThreeSum.java</a>.
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<pre><tt><span class="comment">/******************************************************************************</span>
<span class="comment"> *  Compilation:  javac ThreeSum.java</span>
<span class="comment"> *  Execution:    java ThreeSum input.txt</span>
<span class="comment"> *  Dependencies: In.java StdOut.java Stopwatch.java</span>
<span class="comment"> *  Data files:   </span><span class="url">http://algs4.cs.princeton.edu/14analysis/1Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/2Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/4Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/8Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/16Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/32Kints.txt</span>
<span class="comment"> *                </span><span class="url">http://algs4.cs.princeton.edu/14analysis/1Mints.txt</span>
<span class="comment"> *</span>
<span class="comment"> *  A program with cubic running time. Read in N integers</span>
<span class="comment"> *  and counts the number of triples that sum to exactly 0</span>
<span class="comment"> *  (ignoring integer overflow).</span>
<span class="comment"> *</span>
<span class="comment"> *  % java ThreeSum 1Kints.txt </span>
<span class="comment"> *  70</span>
<span class="comment"> *</span>
<span class="comment"> *  % java ThreeSum 2Kints.txt </span>
<span class="comment"> *  528</span>
<span class="comment"> *</span>
<span class="comment"> *  % java ThreeSum 4Kints.txt </span>
<span class="comment"> *  4039</span>
<span class="comment"> *</span>
<span class="comment"> ******************************************************************************/</span>

<span class="preproc">package</span><span class="normal"> edu</span><span class="symbol">.</span><span class="normal">princeton</span><span class="symbol">.</span><span class="normal">cs</span><span class="symbol">.</span><span class="normal">algs4</span><span class="symbol">;</span>

<span class="comment">/**</span>
<span class="comment"> *  The </span><span class="keyword">&lt;tt&gt;</span><span class="comment">ThreeSum</span><span class="keyword">&lt;/tt&gt;</span><span class="comment"> class provides static methods for counting</span>
<span class="comment"> *  and printing the number of triples in an array of integers that sum to 0</span>
<span class="comment"> *  (ignoring integer overflow).</span>
<span class="comment"> *  </span><span class="keyword">&lt;p&gt;</span>
<span class="comment"> *  This implementation uses a triply nested loop and takes proportional to N^3,</span>
<span class="comment"> *  where N is the number of integers.</span>
<span class="comment"> *  </span><span class="keyword">&lt;p&gt;</span>
<span class="comment"> *  For additional documentation, see </span><span class="keyword">&lt;a</span><span class="normal"> </span><span class="type">href</span><span class="symbol">=</span><span class="string">"http://algs4.cs.princeton.edu/14analysis"</span><span class="keyword">&gt;</span><span class="comment">Section 1.4</span><span class="keyword">&lt;/a&gt;</span><span class="comment"> of</span>
<span class="comment"> *  </span><span class="keyword">&lt;i&gt;</span><span class="comment">Algorithms, 4th Edition</span><span class="keyword">&lt;/i&gt;</span><span class="comment"> by Robert Sedgewick and Kevin Wayne.</span>
<span class="comment"> *</span>
<span class="comment"> *  </span><span class="type">@author</span><span class="comment"> Robert Sedgewick</span>
<span class="comment"> *  </span><span class="type">@author</span><span class="comment"> Kevin Wayne</span>
<span class="comment"> */</span>
<span class="keyword">public</span><span class="normal"> </span><span class="keyword">class</span><span class="normal"> </span><span class="classname">ThreeSum</span><span class="normal"> </span><span class="cbracket">{</span>

<span class="normal">    </span><span class="comment">// Do not instantiate.</span>
<span class="normal">    </span><span class="keyword">private</span><span class="normal"> </span><span class="function">ThreeSum</span><span class="symbol">()</span><span class="normal"> </span><span class="cbracket">{</span><span class="normal"> </span><span class="cbracket">}</span>

<span class="normal">    </span><span class="comment">/**</span>
<span class="comment">     * Prints to standard output the (i, j, k) with i &lt; j &lt; k such that a[i] + a[j] + a[k] == 0.</span>
<span class="comment">     * </span><span class="type">@param</span><span class="comment"> a the array of integers</span>
<span class="comment">     */</span>
<span class="normal">    </span><span class="keyword">public</span><span class="normal"> </span><span class="keyword">static</span><span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="function">printAll</span><span class="symbol">(</span><span class="type">int</span><span class="symbol">[]</span><span class="normal"> a</span><span class="symbol">)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">        </span><span class="type">int</span><span class="normal"> N </span><span class="symbol">=</span><span class="normal"> a</span><span class="symbol">.</span><span class="normal">length</span><span class="symbol">;</span>
<span class="normal">        </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> i </span><span class="symbol">=</span><span class="normal"> </span><span class="number">0</span><span class="symbol">;</span><span class="normal"> i </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> i</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">            </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> j </span><span class="symbol">=</span><span class="normal"> i</span><span class="symbol">+</span><span class="number">1</span><span class="symbol">;</span><span class="normal"> j </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> j</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> k </span><span class="symbol">=</span><span class="normal"> j</span><span class="symbol">+</span><span class="number">1</span><span class="symbol">;</span><span class="normal"> k </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> k</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                    </span><span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">a</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">j</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">k</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">==</span><span class="normal"> </span><span class="number">0</span><span class="symbol">)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                        StdOut</span><span class="symbol">.</span><span class="function">println</span><span class="symbol">(</span><span class="normal">a</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> </span><span class="string">" "</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">j</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> </span><span class="string">" "</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">k</span><span class="symbol">]);</span>
<span class="normal">                    </span><span class="cbracket">}</span>
<span class="normal">                </span><span class="cbracket">}</span>
<span class="normal">            </span><span class="cbracket">}</span>
<span class="normal">        </span><span class="cbracket">}</span>
<span class="normal">    </span><span class="cbracket">}</span><span class="normal"> </span>

<span class="normal">    </span><span class="comment">/**</span>
<span class="comment">     * Returns the number of triples (i, j, k) with i &lt; j &lt; k such that a[i] + a[j] + a[k] == 0.</span>
<span class="comment">     * </span><span class="type">@param</span><span class="comment"> a the array of integers</span>
<span class="comment">     * </span><span class="type">@return</span><span class="comment"> the number of triples (i, j, k) with i &lt; j &lt; k such that a[i] + a[j] + a[k] == 0</span>
<span class="comment">     */</span>
<span class="normal">    </span><span class="keyword">public</span><span class="normal"> </span><span class="keyword">static</span><span class="normal"> </span><span class="type">int</span><span class="normal"> </span><span class="function">count</span><span class="symbol">(</span><span class="type">int</span><span class="symbol">[]</span><span class="normal"> a</span><span class="symbol">)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">        </span><span class="type">int</span><span class="normal"> N </span><span class="symbol">=</span><span class="normal"> a</span><span class="symbol">.</span><span class="normal">length</span><span class="symbol">;</span>
<span class="normal">        </span><span class="type">int</span><span class="normal"> cnt </span><span class="symbol">=</span><span class="normal"> </span><span class="number">0</span><span class="symbol">;</span>
<span class="normal">        </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> i </span><span class="symbol">=</span><span class="normal"> </span><span class="number">0</span><span class="symbol">;</span><span class="normal"> i </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> i</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">            </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> j </span><span class="symbol">=</span><span class="normal"> i</span><span class="symbol">+</span><span class="number">1</span><span class="symbol">;</span><span class="normal"> j </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> j</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                </span><span class="keyword">for</span><span class="normal"> </span><span class="symbol">(</span><span class="type">int</span><span class="normal"> k </span><span class="symbol">=</span><span class="normal"> j</span><span class="symbol">+</span><span class="number">1</span><span class="symbol">;</span><span class="normal"> k </span><span class="symbol">&lt;</span><span class="normal"> N</span><span class="symbol">;</span><span class="normal"> k</span><span class="symbol">++)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                    </span><span class="keyword">if</span><span class="normal"> </span><span class="symbol">(</span><span class="normal">a</span><span class="symbol">[</span><span class="normal">i</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">j</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> a</span><span class="symbol">[</span><span class="normal">k</span><span class="symbol">]</span><span class="normal"> </span><span class="symbol">==</span><span class="normal"> </span><span class="number">0</span><span class="symbol">)</span><span class="normal"> </span><span class="cbracket">{</span>
<span class="normal">                        cnt</span><span class="symbol">++;</span>
<span class="normal">                    </span><span class="cbracket">}</span>
<span class="normal">                </span><span class="cbracket">}</span>
<span class="normal">            </span><span class="cbracket">}</span>
<span class="normal">        </span><span class="cbracket">}</span>
<span class="normal">        </span><span class="keyword">return</span><span class="normal"> cnt</span><span class="symbol">;</span>
<span class="normal">    </span><span class="cbracket">}</span><span class="normal"> </span>

<span class="normal">    </span><span class="comment">/**</span>
<span class="comment">     * Reads in a sequence of integers from a file, specified as a command-line argument;</span>
<span class="comment">     * counts the number of triples sum to exactly zero; prints out the time to perform</span>
<span class="comment">     * the computation.</span>
<span class="comment">     */</span>
<span class="normal">    </span><span class="keyword">public</span><span class="normal"> </span><span class="keyword">static</span><span class="normal"> </span><span class="type">void</span><span class="normal"> </span><span class="function">main</span><span class="symbol">(</span><span class="normal">String</span><span class="symbol">[]</span><span class="normal"> args</span><span class="symbol">)</span><span class="normal">  </span><span class="cbracket">{</span><span class="normal"> </span>
<span class="normal">        </span><span class="usertype">In</span><span class="normal"> in </span><span class="symbol">=</span><span class="normal"> </span><span class="keyword">new</span><span class="normal"> </span><span class="function">In</span><span class="symbol">(</span><span class="normal">args</span><span class="symbol">[</span><span class="number">0</span><span class="symbol">]);</span>
<span class="normal">        </span><span class="type">int</span><span class="symbol">[]</span><span class="normal"> a </span><span class="symbol">=</span><span class="normal"> in</span><span class="symbol">.</span><span class="function">readAllInts</span><span class="symbol">();</span>

<span class="normal">        </span><span class="usertype">Stopwatch</span><span class="normal"> timer </span><span class="symbol">=</span><span class="normal"> </span><span class="keyword">new</span><span class="normal"> </span><span class="function">Stopwatch</span><span class="symbol">();</span>
<span class="normal">        </span><span class="type">int</span><span class="normal"> cnt </span><span class="symbol">=</span><span class="normal"> </span><span class="function">count</span><span class="symbol">(</span><span class="normal">a</span><span class="symbol">);</span>
<span class="normal">        StdOut</span><span class="symbol">.</span><span class="function">println</span><span class="symbol">(</span><span class="string">"elapsed time = "</span><span class="normal"> </span><span class="symbol">+</span><span class="normal"> timer</span><span class="symbol">.</span><span class="function">elapsedTime</span><span class="symbol">());</span>
<span class="normal">        StdOut</span><span class="symbol">.</span><span class="function">println</span><span class="symbol">(</span><span class="normal">cnt</span><span class="symbol">);</span>
<span class="normal">    </span><span class="cbracket">}</span><span class="normal"> </span>
<span class="cbracket">}</span><span class="normal"> </span>

<span class="comment">/******************************************************************************</span>
<span class="comment"> *  Copyright 2002-2015, Robert Sedgewick and Kevin Wayne.</span>
<span class="comment"> *</span>
<span class="comment"> *  This file is part of algs4.jar, which accompanies the textbook</span>
<span class="comment"> *</span>
<span class="comment"> *      Algorithms, 4th edition by Robert Sedgewick and Kevin Wayne,</span>
<span class="comment"> *      Addison-Wesley Professional, 2011, ISBN 0-321-57351-X.</span>
<span class="comment"> *      </span><span class="url">http://algs4.cs.princeton.edu</span>
<span class="comment"> *</span>
<span class="comment"> *</span>
<span class="comment"> *  algs4.jar is free software: you can redistribute it and/or modify</span>
<span class="comment"> *  it under the terms of the GNU General Public License as published by</span>
<span class="comment"> *  the Free Software Foundation, either version 3 of the License, or</span>
<span class="comment"> *  (at your option) any later version.</span>
<span class="comment"> *</span>
<span class="comment"> *  algs4.jar is distributed in the hope that it will be useful,</span>
<span class="comment"> *  but WITHOUT ANY WARRANTY; without even the implied warranty of</span>
<span class="comment"> *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the</span>
<span class="comment"> *  GNU General Public License for more details.</span>
<span class="comment"> *</span>
<span class="comment"> *  You should have received a copy of the GNU General Public License</span>
<span class="comment"> *  along with algs4.jar.  If not, see </span><span class="url">http://www.gnu.org/licenses.</span>
<span class="comment"> ******************************************************************************/</span>
</tt></pre>

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Last updated: Mon Mar 21 10:51:08 EDT 2016.
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